Roller jacks for latching two elements articulated together have been known for a long time, these jacks being used particularly in automobiles for seats comprising a back portion with an adjustable inclination and an adjustable base portion (centering of the position of the sitting portion of the seat) and also for adjusting in height and inclination the head-rests as well as the thigh cushions of the respective seat.
This is, for example, the case with the device disclosed in European Document 0 419 336 which shows a mechanical jack having a rectilinear or circular displacement, in which a toothed roller cooperates with a smooth bar with respect to a casing enclosing two reversed V-shaped members, the central portions of which form a toothed ramp cooperating with a blocking cam.
From European Document 0 234 160 a rectilinear jack is known which shows a mobile rod extending through a casing or cage in which are placed, as in the above case, two V-shaped members, the inner portion of which is not toothed, but cooperates also with smooth rollers for enabling a blocking or unblocking of the jack with assistance of a cam.
French Document 2 574 721 shows the blocking of a continuous linear adjusting device comprised of two opposed rectilinear members which terminate each in two assemblies of interconnected horizontal strips which can be blocked by rollers with assistance of a double cam. The rollers are also housed inside reversed V-shaped members, and the entire assembly is finally placed inside a casing.
French Document 2 547 078 relates to a device of the same nature as the above devices, but is of a more complicated construction.
Indeed, all these mechanisms are more or less satisfactory, but they all suffer from a major disadvantage which is that, when an accident occurs to the vehicle equipped with these roller jacks, i.e. when it is absolutely necessary to obtain an instantaneous blockage and securing, it has been found that the members which are in motion, and particularly the rollers, cause the metal to flow on the sliding bar, thereby preventing an instantaneous blockage. Furthermore, the rollers have a tendency to slide before blocking.
This represents a considerable danger, and is the reason why means have been considered for preventing such a phenomenon which presents intolerable extra hazards upon a frontal or lateral impact on the vehicle.